As noted in my earlier patents, portable shelters have been in existence since prehistoric times. Recently, there has been an increase in the sophistication, quality and construction of portable structure apparatus. Relatively large area, temporary shelters which may be stored in the small collapsed state but which may be expanded with a minimum amount of effort and sturdy, large area shelters are known and are discussed in my earlier three patents as well as the references known in the art. These shelters typically employ a framework that supports a lightweight fabric roof or covering for shade, for privacy, or for protection against natural elements such as wind and rain. Side panels may also be used for background display, in the form of protective netting against insects, for privacy and the like. Often, the shelters to which the present invention is directed are those which are used for purposes of recreation, fairs, bazaars, outdoor exhibitions and food and beverage vending, to name a few.
As noted above, one response to the need for portable shelters was shown in my U.S. Pat. No. 4,641,676. This patent discloses a portable canopy structure which has a framework that may be collapsed into a stored state yet which may be expanded and erected for use. The framework includes a plurality of upright support members, the adjacent ones of which are connected by means of scissor assemblies comprising either single or dual scissor units connected in end-to-end relation. A flexible covering extends over the framework. In several of the embodiments, a central support is provided for the covering in the form of a central post so that the covering is supported in a dome-like manner. In another embodiment, no central post structure is shown. The invention described in U.S. Pat. No. 4,641,676 is also somewhat to that described in U.S. Pat. No. 4,607,656 issued 26 Aug. 1986 to Carter.
A problem experienced by the structures shown in patent '676 (Lynch) and in patent '656 (Carter) is that the edge scissor assemblies which extend between adjacent support members are often subjected to lateral forces which tend to decrease their stability. Where the scissor assemblies are connected to each other and to the corner supports, compression mounts were used which, if tightened, inhibited the scissoring action and were subjected to shear forces upon lateral deflection. It was often found that the connecting bolts could be bent or broken by excessive lateral deflections.
The structure described in my patent '676 was greatly improved by that disclosed in my U.S. Pat. No. 4,779,635 issued 25 Oct. 1988. In this patent, the canopy structure outwardly biased its corner support members so that the framework interconnecting adjacent corner support members was placed in tension as opposed to compression, which was the case in my patent '676. Nonetheless, the assembly shown in my patent '635 was still subject to improvement in the scissor bar interconnections. Likewise, the structure shown in patent '884 while providing a very useful canopy of an auto-erect feature relied on similar scissor bar interconnecting bolts which, while quite workable, had the disadvantages indicated above.
In an effort to further stabilize my collapsible canopy structures and meet the aforementioned problem, I developed a stabilization bar for use with these scissor assemblies. The construction and attachment of this stabilization bar is described thoroughly in my U.S. Pat. No. 4,885,891 issued 12 Dec. 1989 for reinforcement member for an extendible scissors truss. It was noted in that patent that conventional extendible scissor trusses have great strength and may be very stiff in resisting loads resulting from forces in the plane of their truss cells and related moments normal to those cells, but that such scissor assemblies are generally weak and relatively flexible when subjected to side loads imposed by forces acting normal to the plane of the truss cells and weak with respect to the related moments lying in the planes of the cells. This problem was solved, in part, by the inclusion of a reinforcement member having end portions which extend along side a facing pair of scissor bars of two scissor units which are connected in end-to-end relation. A linking portion extends between the end portions and rigidly joins them. This structure thus defines lever members which produce moment couples on the truss members with these lever members then resisting torsional and bending stress forces.
While the structure described in my patent '891 works quite well, it adds additional complexity to the structure the collapsible unit to which it is attached and thus increases manufacturing costs and weight. There therefore remained a need for still further improvements and stabilizing truss assemblies, particularly where those truss assemblies are incorporated into collapsible canopy structures. There is a further need recognized when products are manufactured according to my above referenced patents in simplifying the mounting of the scissor bar elements, one to another into scissor units and the resulting scissor units into interconnected scissor or truss assemblies, and in the connection of such truss assemblies in a pivotal expandable/collapsible manner to respective corner and intermediate supports. There is further a recognized need for interconnections which would be more resistive to shear and bending moments.